Measurement of fiber diameters with high precision

摘要

Methods for measuring the diameters of transparent filaments with high precision, e.g., RMS standard deviations of less than 0.02 microns, are provided. The methods involve determining the average spatial frequency omega of the far-field interference pattern produced by illuminating the filament with a beam of laser light. The average spatial frequency is determined by performing a fast Fourier transform (FFT) on the interference data to obtain a coarse estimate for the average and then performing a set of discrete sequence Fourier transforms (DSFTs) in the region of the coarse estimate to obtain the desired high precision estimate of the average. Efficient on-line processing procedures are provided so that real time measurements can be performed on, for example, a moving optical waveguide fiber, at rates of 500 measurements/second and above.